In manufacturing semiconductor devices, some regions of a workpiece are selectively removed in some cases. A kind of a workpiece, which is subjected to such a processing, includes a first region formed of silicon oxide and a second region formed of silicon. A processing of selectively removing the first region from such a workpiece is disclosed in Japanese National Phase Patent Laid-Open Publication No. 2007-515074.
In the processing disclosed in Japanese National Phase Patent Laid-Open Publication No. 2007-515074, (NH4)2SiF6 is produced by a reaction of HF and NH3 and silicon oxide in the first region. That is, some regions including a surface of the first region are denatured by the reaction. In addition, when the workpiece is heated, denatured (NH4)2SiF6 is thermally decomposed. In the processing disclosed in Japanese National Phase Patent Laid-Open Publication No. 2007-515074, the region formed of silicon oxide is selectively removed through denaturation and thermal decomposition.
Recently, attempts have been made to perform a processing in which the processing disclosed in Japanese National Phase Patent Laid-Open Publication No. 2007-515074, i.e., the selective removal by denaturation and thermal decomposition is performed using plasma. For example, Japanese Patent Laid-Open Publication No. 2008-16869 discloses a processing in which a region formed of silicon oxide is denatured by plasma of a gas containing H2, N2, and NF3, and the denatured region is removed by thermal decomposition. In addition, Japanese National Phase Patent Laid-Open Publication No. 2013-503482 discloses a processing in which a carbon-containing film is denatured by plasma of a gas containing NH3 and NF3, and a denatured region is removed by thermal decomposition.